In order to access certain types of hydrocarbons in the earth, it may be necessary or desirable to drill wells or boreholes in a certain spatial relationship with respect to one another. Producing unconventional oil such as shale oil, heavy oil, or bitumen, may require technology that utilizes an arrangement of boreholes. For example, heavy oil may be too viscous in its natural state to be produced from a conventional well, and, thus, an arrangement of cooperative wells and well features may be utilized to produce such oil. Indeed, to produce certain types of unconventional oil, it may be desirable to drill numerous boreholes in a patterned arrangement such that some wells can be used to condition a formation and other wells can be used to produce oil from the formation. Thus, in the process of arranging such a pattern of boreholes, it may be desirable to drill a borehole such that it has a specific location relative to one or more previously drilled boreholes.
As a specific example of utilizing an arrangement of wells to access unconventional oil, heating an oil-bearing formation to very high temperatures with an arrangement of heating wells can facilitate cracking heavy oil or bitumen into lighter hydrocarbons that can be more easily produced due to their reduced viscosity. Similarly, shale oil may be produced from kerogen by a process that includes providing very high temperatures in the shale formation via an arrangement of wells. Such in situ upgrading and conversion processes generally require a large number of heater wells to raise the formation temperature to several hundred degrees C. Indeed, this may require hundreds of heater wells drilled in a dense pattern. Also, there are numerous other situations that may benefit from a densely packed arrangement of wells.
Well patterns utilized for accessing certain types of oil may have an inter-well spacing of only a few meters. To achieve certain well pattern arrangements, each well may need to be kept within what is essentially an imaginary cylinder within a formation, wherein each imaginary cylinder has a radius of a few meters (e.g., 1.5 meter radius). Using many conventional techniques, it may be difficult to accurately drill one well in a specified relationship relative to another well. Indeed, standard measurement while drilling (MWD) direction and inclination measurements are usually too inaccurate to maintain proper spacing and relative positioning between two wells over a substantial distance. In part, this is because the location of each well becomes more uncertain as the length of the well increases. For example, the uncertainties may be represented as ellipses at different well lengths that represent the area in which the well may be located at a particular point. These ellipses increase in area with drilled depth. Thus, it may be difficult to accurately position wells relative to one another. Indeed, if the ellipses for a pair of wells overlap, there is potential for a collision between the wells.